Mic McPherson offers the service of modifying the Marlin 336 to cycle longer cartridges. He will modify the Marlin to handle cartridges up to 2.73" in overall length. He will also modify Win 94's but doesn't promise much improvement there.
I took a look at the two actions and frankly, to my simple mind, the Win 94 looked easier to modify than the 336, so I had a go at it with my 356 Winchester. I bought a pre-64 carrier to modify because it is a stronger forging whereas the post 64 carrier is cast. My 356 would cycle a COL of 2.57" which is the length I use for the RCBS 35-200-FN. My two heavyweight loads measure 2.69" with the Saeco 352 and 2.71" with the NEI 290-GC. I therefore cut the lug on top of the carrier back that the bolt catches to raise the carrier and the cartridge stop shoulder on the carrier back .140". The pre-64 carrier is slightly larger in nearly every dimension than the post 64 carrier. I spent about four hours narrowing it and relieving various places so it would move freely inside the receiver. This is a picture of the two carriers with the modified pre-64 carrier in front:
The post-64 carrier screw limits the lever travel and therefore the bolt travel and when Winchester went to the cast carrier they added a bridge to tie the two sides of the carrier together that also limits bolt travel. The bridge and the screw have to be eliminated. This picture shows the open back of the pre-64 carrier and the bridge on the post 64 carrier. It also shows the original screw and the screw I cut down for the left side. I used a roll pin for the right side of the carrier to pivot on:
The little inverted V shaped cam that the carrier spring rides on to hold the carrier up or down as needed is also different pre- and post-64. I spent hours grinding that cam on the pre-64 carrier and trying it in the rifle. I finally got it to work but it weren't easy!
Everything worked as expected to this point and the rifle would cycle the 2.71" ammo as long as I held the lower link up while working the lever. Huh? Yes, if I let the lower link drop all the way the lever would lock when I tried to pull it back to feed a cartridge into the chamber. The post-64 lever has an L shaped slot that the lever pivot pin rides in. When the link dropped the pin would get into the bottom of the L and lock the lever. This photo shows the link at its lowest point where the lever would lock:
There are two lugs on the front of the lower tang that stop the locking bolt's downward travel. Since the lower link hangs on the bottom of the locking bolt I tried building up the two little lugs on the lower tang with weld to limit the locking bolt travel and keep the lower link from dropping to the point where the pivot pin would get into the bottom of the L. Didn't work! It was so close that if I pulled down on the lever it would work, but if I had upward pressure on the lever, which is normal, it would lock. Another thing that happened was that the heat of the welding shrank and distorted the part of the lower tang that the lever detent engages and I had to rework that section also.
After a bit of head scratching I decided to add a piece of metal to the bottom of the lower link that the front of the trigger loop would hit when the lever is all the way forward and thereby push the lower link up. That piece of metal is in the last picture. Worked like a charm! Here it is attached to the lower link and you can see how it pushes the lower link up to keep the pin out of the bottom of the L. You can also see the end of the roll pin in the side of the receiver:
I left out some whys and wherefors in this account. It ain't quite as simple as it looks but this is the gist of it. And it won't be this simple to modify a pre-64. I only went for a COL of 2.71" but I think I can equal Mic's 2.73". It's a measly .020" more.
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Originally Posted by 4fingermick
